This type of cutoff which is described, for example, in French Pat. No. FR-A-2 087 317, is particularly suitable for a dipped beam as required, for example, in the United States of America and as defined by standard SAEJ 579 C.
In order to satisfy this standard, the profile of the cutoff on a standardized projection screen is defined approximately by two horizontal half-lines situated on either side of the headlight axis, with the right-hand side half-line being at horizon level and the left-hand side half-line being offset by about 1.5% below the horizon. In addition, the region of maximum illumination (concentration spot) must be offset towards the right relative to the headlight axis.
The main light beam must have a concentration spot which is approximately centered on the travel axis.
In the prior art, main and dipped beam headlights of this type generally include a lamp having two horizontal filaments which are transversely disposed relative to the headlight axis and which are offset from each other in two directions perpendicular to the headlight axis, i.e. both sideways and vertically.
The associated reflector generally includes a reflecting surface in the form of a paraboloid of revolution whose focus in situated level with the two filaments and halfway between them in a vertical direction. Thus, it is possible to obtain a dipped beam which is situated for the most part beneath a horizontal cutoff and which has a concentration spot which is centered approximately on the travel axis.
However, a non-negligible residual portion of the beam is situated above the cutoff and requires the headlight glass to include deflector prisms or ribs of considerable thickness, thereby giving rise to molding difficulties, particularly when the glass is literally made of glass. In addition, the edges of the prisms are liable to give rise to parasitic light rays which are upwardly directed and which may dazzle oncoming drivers.
Further, since it is desirable for the light beam to be of small thickness in a vertical direction prior to passing through the closure glass, still for the purpose of avoiding the need to provide very thick vertical-deflection stripes in the deflector glass, a parabolic reflector is used whose focal length is relatively long. However, increasing the focal length of a reflector of given outline considerably reduces the amount of light flux emitted from the filaments which is recovered by the reflector, i.e. leads to a reduction in light yield.
The present invention seeks to mitigate the drawbacks of the prior art and to provide a main beam and dipped beam headlight in which no or substantially no vertical deflection of the light rays needs to be performed by the closure glass, and in which the beam that is obtained satisfies the photometric conditions required, in particular, by the United States. Another aim of the present invention is to obtain light beams which are relatively thin prior to passing through the closure glass, without, however, greatly reducing the light yield from the headlight.